FIG. 1 is a network architecture of a Universal Mobile Telecommunications System (UMTS). UMTS system is composed of a User Equipment (UE), a UMTS Terrestrial Radio Access Network (UTRAN) and a Core Network (CN). UTRAN includes at least one radio network sub-system (RNS), each of which includes one Radio Network Controller (RNC) and one or more base stations (Node Bs) managed by the RNC. One or more cells exist in one Node B.
FIG. 2 is an architecture of radio protocol layers used in UMTS. The radio protocol layers exist as a pair in a UE and UTRAN, and handle data transmission over radio interfaces. Explaining each of the radio protocol layers, first, a first layer as a physical (PHY) layer serves to send data over a radio interface using various radio transmission techniques. The PHY layer is connected to an upper layer, called a Medium Access Control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel. Transport channels are categorized into dedicated transport channels and common transport channels depending on whether a channel is shared.
The second layer includes the MAC layer, a Radio Link Control (RLC) layer, a Packet Data Convergence Protocol (PDCP) layer and a Broadcast/Multicast Control (BMC) layer. First, the MAC layer maps various logical channels to various transport channels, and also perform a logical channel multiplexing for mapping several logical channels to one transport channel. The MAC layer is connected to an upper layer, called a RLC layer, via a logical channel. The logical channels are categorized into control channels for sending information of a control plane, and traffic channels for sending information of a user plane. The MAC layer is divided, according to a type of a transport channel to manage, into MAC-b sublayer, MAC-d sublayer, MAC-c/sh sublayer, MAC-hs/ehs sublayer and MAC-e/es or MAC-i/is sublayer. The MAC-b sublayer manages a Broadcast Channel (BCH) as a transport channel for managing broadcasting of system information, and the MAC-c/sh sublayer manages Forward Access Channel (FACH) as a common transport channel shared with other terminals, and MAC-d sublayer manages a Dedicated Channel (DCH) as a common transport channel for a specific terminal. In addition, for supporting a high-speed data transmission in downlink and uplink, the MAC-hs/ehs sublayer manages a High Speed Downlink Shared Channel (HS-DSCH) as a transport channel for high-speed downlink data transmission, and MAC-e/es or MAC-i/is sublayer manages an Enhanced Dedicated Channel (E-DCH) as a transport channel for high-speed uplink data transmission.
The RLC layer handles guarantee of QoS of each radio bear (RB) and data transmission. The RLC provides one or two independent RLC entities for each RB for the purpose of RB-specific QoS. The RLC layer manages segmentation and concatenation of data received from an upper layer to appropriately adjust a data size such that a lower layer can send data over an interface. Also, the RLC layer provides three operation modes, including a transparent mode (TM), an un-acknowledged mode (UM) and an acknowledged mode (AM), so as to guarantee various qualities of service (QoS) requirements of each radio bearer (RB).
A packet data convergence protocol (PDCP) layer located at the second layer is used to efficiently transmit IP packets, such as IPv4 or IPv6, on a radio interface with a relatively small bandwidth. For this purpose, the PDCP layer reduces the size of an IP packet header which is relatively great in size and includes unnecessary control information, namely, performs a function called header compression. Accordingly, only necessary information can be included in the header part of data for transmission, so as to increase a transmission efficiency of a radio interface. The PDCP layer is present on a packet-switched (PS) domain because the header compression is its basic function. For providing an effective header compression function for each packet service, one PDCP entity exists for each RB. Also, if the PDCP layer is present on a voice domain, the header compression function is not provided.
Among others, the BMC layer is present above the RLC layer in the second layer, and performs some functions, such as scheduling of a cell broadcast message and broadcasting to terminals located within a specific cell.
The RRC layer located at the uppermost portion of the third layer is only defined in the control plane. The RRC layer controls parameters of the first and second layers and also controls logical channels, transport channels and physical channels, in relation to configuration, re-configuration and release of Radio Bearers (RBs). Here, the RB denotes a logical path that the first and second layers provide for data transmission between the terminal and the UTRAN. In general, the establishment of the RB refers to stipulating the characteristics of protocol layer and channel required for providing a specific service, and setting the respective detailed parameters and operation methods.